On Thu, Aug 27, 2020 at 07:42:43PM +0200, Martin Kepplinger wrote: > On 26.08.20 09:48, Martin Kepplinger wrote: > > On 24.08.20 22:13, Alan Stern wrote: > >> Martin: > >> > >> (I forgot to ask this question several weeks ago, while you were running > >> your tests. Better ask it now before I forget again...) > >> > >> I suspect the old runtime-PM code in the block layer would have worked > >> okay in your SD cardreader test if the BLK_MQ_REQ_PREEMPT flag had not > >> been set. Do you know why the flag was set, or what line of code caused > >> it to be set? > > > > Correct. if not set, I could handle all I need in the scsi error path. > > this thread becomes a bit confusing. I thought about REQ_FAILFAST_DEV > but you're talking about something different. > > the only place I see BLK_MQ_REQ_PREEMPT getting passed on is in > __scsi_execute() which is the case when mounting/unmounting. At least > that about the only place I can find. Ah yes, I see what you mean. > I remember *only* your block pm fix would let me mount/unmount, but not > use files yet (REQ_FAILFAST_DEV and so on). > > When I revert your fix and remove BLK_MQ_REQ_PREEMPT from being passed > on to blk_get_request() in __scsi_execute(), that line gets executed > exactly once during startup and I'm missing the /dev/sda device from the > cardreader then. > > Is this what you're asking? Not quite sure, but it doesn't matter. Removing BLK_MQ_REQ_PREEMPT in __scsi_execute() is probably not a safe thing to do. Instead, look at sd_resume(). That routine calls __scsi_execute() indirectly through sd_start_stop_device(), and the only reason it does this is because the sdkp->device->manage_start_stop flag is set. You ought to be able to clear this flag in sysfs, by writing to /sys/block/sda/device/scsi_disk/*/manage_start_stop. If you do this before allowing the card reader to go into runtime suspend, does it then resume okay? (Yes, I know you still won't be able to read it because of the FAILFAST flag. I just want to know if the runtime resume actually takes place.) Alan Stern
